1. Field of the Invention
The present invention relates to virtual networks, and more specifically to the design apparatus and method for virtual local area networks (VLANs) of multiple spanning tree protocol (MSTP).
2. Description of the Related Art
According to a known spanning tree technology as described in technical paper “A Study of VLAN Design Algorithm for Transparent LAN Service with MSTP”, Electronics, Information and Communications Institute of Japan, B-14-5, page 467, September 2002, a network management system is provided for receiving a network configuration request from a communications network and designing a VLAN spanning tree topology in accordance with information contained in the request such as the identities of VLAN member nodes and the volumes of their unicast and broadcast traffic, based on link cost represented by link utilization factor. For each network configuration request, the network management system builds up a number of VLAN topologies for the same group of VLAN member nodes. In each of the VLAN topologies, the VLAN member nodes are interconnected by a minimum number of links in a spanning tree that is arbitrarily different from the spanning tree of every other VLAN topologies. For each VLAN topology, a total of link costs is calculated and compared with the total link cost of other VLANs. The VLAN topology of the minimum total link cost is selected for the received network configuration request. The selected spanning tree is downloaded from the network management system to the communications network using the multiple spanning tree protocol (MSTP) and the network devices are configured and their link costs are set according to the designed traffic and link costs.
However, since the total sum of link costs is the only factor for determining a VLAN topology, the prior art technique is not satisfactory in terms of dispersion of load across the network.